Can someone explain a couple of very simple concepts to me - I'm interested in mobile devices running android and how they are identified over networks. Some scenarios:
Device is connected over WiFi - presumably the device has a standard IP address as with any host and can communicate with any other android host over TCP/IP (assuming it knows the participating device's IP?
Device is connected over bluetooth - how are devices identified in this case?
Device is connected over mobile operator's network - this is the one I'm interested in and confused by - is there anyway for two or more devices to discover each other and communicate via the mobile operator's network? How does a device communicate with a backend server in this scenario? In other words, how do apps and devices communicate when not connected to a WiFi network?
Thanks for any advice..
I'm only sure about the bluetooth thing, so i only answer this part:
The Bluetooth interface on your device has an MAC adresse. So while communicationg over Bluetooth you can assume that this MAC adresse is a unique identifier for a specific device. You can also reach other devices by establishing a connection over this MAC adress- However, to get this mac adress in the first place, you have to know it from somwhere, or you have to search for other bluetooth devices in the reachabla area before.
WiFi and 3g both attach the [mobile] device to the internet so it can make internet connections. 3G assigns a publicly addressable IP to the device, so one could, presumably open a server socket and listen for connections. The client would have to know the mobile IP, which may change quite frequently.
Bluetooth is more geared toward close-proximity. Devices in the vicinity can be connected to, after you have paired with them, which requires the cooperation of both devices which are to communicate.
If the goal is to produce an application which connects to nearby devices, I can think of the following ideas:
3g: all devices running the client register their position with a central database server. If the server detects that two clients are in close proximity, let them know so they can connect through the internet or through the server
WiFi: you could use the same idea as 3g, or use broadcast/multicast packets to broadcast your presence. Other apps can listen for those broadcasts and discover which other devices are near.
Bluetooth: A little trickier, as a device must be placed into discoverable mode in order for others to "see it". Discoverable mode is a temporary state and only lasts about 30 seconds (at a time).
Related
I have 6 android tablets, and i want to connect them via a cable/wire, so that they can send messages to one another. (perhaps similar to way PCs may be networked with each other)
Once connected, apps running on the devices can exchange messages with each other via sockets or any other protocol. What are the best options?
Connecting devices over wi-fi is an option too, but then internet is not guaranteed in this scenario, and devices may be very far of from each other for any near field communication.
You can use usb->ethernet adapters and connect via LAN
Connecting devices over wi-fi is an option too, but then internet is
not guaranteed in this scenario, and devices may be very far of from
each other for any near field communication.
as long as all your devices and server (if any) are on same LAN or simply everything is connected to same hotspot you need not to worry about internet
I want to work with Wifi connection via Android Devices (for example I want to send a command with my device to home router via Internet and my router send this command to a wifi module) when I refer to Developer Android APIs, I see a section that named "Wi-Fi Peer-to-Peer". what differences exist between wifi (working android devices with access point like home router) and "Wi-Fi Peer-to-Peer". Is "Wi-Fi Peer-to-Peer" same wifi Direct ? why Google didnt discusses about simple wifi ? please help.
WiFi P2P (Peer-to-Peer) and WiFi Direct are both the same thing.
There are two main differences between "normal" WiFi and WiFi P2P (from the developer's point of view):
A WiFi p2p connection (something you establish from code) is a direct connection between two devices. You can understand it as a sort of temporary (created for the time of the connection) "normal" WiFi network created for the purpose of communicating those two devices. A "normal" WiFi connection basically translates to a situation when a device is connected to a broadcasted (by some device - e.g. home access point, or a smartphone) WiFi network. This all basically means that to send data between two devices using WiFi P2P, those devices DO NOT have to be connected to the same WiFi network (as long as those devices know how to connect to each other using wifi p2p). Unfortunatelly good news with WiFi P2P end right here, because:
Designing a WiFi P2P connection based system is extremely difficult if you want to make it at least reasonably robust. This is mostly due to the lack of documentation on that subject (in Android Dev), and due to Android's WiFi p2p unpredictability (I know what I'm talking about - I was recently desigining such system).
You're wrong saying that Google didn't discuss "simple" WiFi. You just need to remember that connecting to "simple" WiFi is just not that complicated, so they didnt have to do a guide like they did for WiFi P2P. All information considering "normal" WiFi are there (at Android Developer), its just spread over many classes.
Tell me what you think is not discussed?
Also you should try to describe the exact thing your application needs to do (with WiFi), so I can maybe give you a hint whether you should try your luck with WiFi P2P or not.
I am maintaining a small app related to wifi networks. It tests internet connectivity when the phone connected to a wifi network.
While testing and using the app in a place with two neighbouring wifi networks (different SSIDs) with slightly overlapping coverage with a HTC Desire running Android 2.2.2, the sequence of disconnecting and connecting when moving from wifi A to B seems to be:
Disconnect from wifi A
Connect to wifi B
Now with a Fairphone running 4.2.2, the sequence seems to be:
Connect to wifi B
Disconnect from wifi A
Does this mean that unlike the HTC Desire, the Fairphone does some sort of roaming and first connects to the wifi whose signal became stronger than the one of the current wifi connection, and then drops the "old" wifi connection?
I am asking this question because if my observations are correct, this has some implications on the app's behaviour, i.e. it should not consider the last wifi connectivity event but rather check the actual state of wifi connectivity regardless if the last event was "connected" or "disconnected".
On android, as on many linux flavors, wpa_supplicant controls roaming behavior. You could look into it so to see what it is doing.
Specifically to answer your question, it is possible for a WLAN Device (in linux), to use different types of drivers:
SoftMAC: MLME (Media Access Control (MAC) Sublayer Management Entity) is managed in software.
FullMAC: MLME is managed in hardware.
Particularly some of the MLME functions are:
Authenticate
Deauthenticate
Associate
Disassociate
Reassociate
So differences are to be expected in some of this mechanisms on different devices and versions of Android (driver types, wpa_supplicant).
The correct 802.11 behavior for roaming is to send an Reassociation request to the newly selected AP. Clients that first Disassociate from an AP to later Associate with a new AP actually do not support 802.11 roaming and use some sort of fake-roaming through a SoftMac approach.
In standard roaming packets sent to a station do not get lost and are forwarded from one AP to the roamed AP in order for the roaming station to receive them.
I'm doing a research because I want to develop an app to which different devices connect.
The app can be an Android or iPhone smartphone. It will be for mountain equipment devices and sensors, so no wifi router is availabe. It needs long range, so Bluetooth is not an option.
I'm thinking on creating a hotspot in the smartphone and connect the devices to this hotspot. In this case, I'm thiking of this way of doing it:
Programatically create the hotspot in the smartphone. In Android, like this: http://www.whitebyte.info/android/android-wifi-hotspot-manager-class
Set up the name of the hotspot in the devices so they know where to connect. Pressing a button, they connect to the hotspot.
The android device broadcasts its IP, so devices know where to connect.
Devices connect and send the data.
I think this could be a real scenario, but I'm worried about:
Maybe there's a design flaw in my scenario that I'm not seing.
Batteries on the devices: how do batteries behave through "intensive" use of WIFI? (sending small amount of bytes of data every five minutes, e.g.).
The ability to replicate this scenario on an iPhone. Can it be done, or should the user manually create the hotspot to do this?
Any other feedback that I couldn't be thinking of.
Thanks.
Yes, on Android all of that can be done and should work fine.
Yes, you can programatically configure the hotspots info in the client.
Another way to make the connection (other then hotspot broadcasting its IP) is for the hotspot to reads it ARP cache, i.e. parse the cache to find the IP of all of the clients connected.
Battery could be a problem. That doesn't really sound like 'intensive' use of the wifi, but it will still consume a fair bit of battery (I find that even just having the hotspot enabled draws the battery).
I don't know the answer for iPhone.
Since I don't have an Android 4.0 device I haven't been able to test this myself. Also I wonder if connecting device A (a smartphone) to device B (a wifi direct capable device) using Wifi direct would mean that device A would assume it is provided with internet from device B (tethering?). I am trying to make an application for device A that would communicate with a device B that does NOT provide internet, thus it would be interesting to know if such a scenario would lead to device A losing internet connectivity for the duration of the connection. Is the situation different depending on if device A is connected to internet through an AP or through 3G/4G?
Perhaps using Bluetooth would be a solution, but in my case security is an issue, and it seems to me that Wifi direct provides stronger security (WPA2).
Any info would be helpful!
/S
On Android, Wi-Fi Direct doesn't interfere with your connection to the Internet (Wi-Fi or 3G/4G). A problem may be that once your turn on the Wi-Fi (to enable Wi-Fi Direct, your phone will try to connect to one of the saved available networks and will disable your 3G connection. That is because Android (by default) doesn't support dual connection (via both Wi-Fi and 3G/4G), but there is some applications around that claim that they can provide such functionality.